Interference estimation circuit and method

ABSTRACT

The present application provides an interference estimation circuit which includes a signal generator, a first symbol extractor and a first mixer. The signal generator generates an orthogonal signal orthogonal to partial symbols of a plurality of pilot signals. The first symbol extractor extracts partial symbols of a first decoded signal decoded from a received signal wherein the first decoded signal contains one of the plurality of pilot signals, and includes an input node for receiving the first decoded signal and an output node for outputting a first extracted signal. The first extracted signal is substantially orthogonal to the orthogonal signal. The first mixer is coupled to the signal generator for receiving the orthogonal signal and to the first symbol extractor for receiving the first extracted signal, and outputs a first mixed signal of the orthogonal signal and the first extracted signal for interference estimation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a direct sequence spread spectrum communicationsystem, and more particularly to a code division multiple accessreceiver.

2. Description of the Related Art

Various wireless communication systems have adopted various schemes forsupporting as many simultaneous users as possible. Code DivisionMultiple Access (CDMA) is one of such schemes. CDMA is a techniqueemployed in spread spectrum communication systems that allows multipleusers to simultaneously share the same frequency. In CDMA systems, awideband spreading signal is used to convert a narrowband data signalinto a wideband signal for transmission. Direct sequence spread spectrum(DSSS) systems use a pseudo noise (PN) sequence to spread the datasignal into a wideband signal.

The signal to interference ratio (SIR) estimation is an importanttechnique for CDMA receivers. In a CDMA receiver, many modern componentsutilize the SIR estimated result as a comparison threshold factor or asa decoding parameter, such as Multi-Path Searcher, Cell Searcher, TurboDecoder, or Power controller. Especially in a power controller, the SIRestimation error is closely related to the power control error andtherefore directly related to the service capacity. More precise SIRestimation improves system performance, and relies on more preciseinterference estimation.

Interference estimation estimates the interference power existing inreceived signals. The interference may include additive white Gaussiannoise (AWGN) existing in passing channel, interference from otherco-channel signals, interference from multi-path effects, interferencefrom non-ideal demodulation process, and/or any other form ofinterference. One interference estimation method firstly re-builds thepure-signal component of the received signal in the receiver, and thensubtracts the re-built pure-signal component from the total receivedsignal to obtain an estimated interference component power. This method,however, is highly dependent on channel estimation precision to rebuilda reliable pure-signal component. Precise channel estimation isdifficult in fast fading channels because the channel estimationalgorithm may not be reliably for tracking the rapidly varying channeleffect.

Another method utilizes the characteristics of orthogonal spreading codein the CDMA system. Because CDMA systems use orthogonal codes todistinguish different channels or users, and there always exists un-usedorthogonal code, this method uses one un-used code to de-spread receivedsignal for canceling the pure-signal component. For example, assuminginterference is estimated by common pilot channel, and transmitdiversity exists. In WCDMA systems with transmit diversity mode, commonpilot symbols are orthogonally transmitted on 2 antennas as shown inFIG. 1. Another pattern, orthogonal to pilot symbol patterns on bothantennas, can cancel the pure-signal by de-patterning the receivedsymbol as shown in FIG. 2. In FIG. 2, pattern 21 is the patterntransmitted by antenna 1, pattern 22 is the pattern transmitted byantenna 2, and pattern 23 is the pattern for de-patterning the receivedsymbol. Assuming that pattern 21 and pattern 22 are transmitted in astatic channel, H_(ant1,0)˜H_(ant1,9) are the channel response of eachsymbol of slot 0 in pattern 21, and H_(ant2,0)˜H_(ant2,9) are thechannel response of each symbol of slot 0 in pattern 22, thenH_(ant1,0)=H_(ant1,1)= . . . =H_(ant1,9) and H_(ant2,0)=H_(ant2,1)= . .. =H_(ant2,9). The averaged de-patterning output for antenna 1 is 0, andthe averaged de-patterning output for antenna 2 is A²·H_(ant2,0)/5.Because no channel estimation result is required, the described methodis generally more robust in fast-fading channels. Although the methodperforms better in a high speed environment, large interference powerestimation offset still occurs when the Doppler frequency is high asshown in FIG. 3. In FIG. 3, assuming that pattern 21 and pattern 22 aretransmitted in a fast-fading channel, Δ_(ant1), H_(ant1,0)˜H_(ant1,9)are the channel shift and channel response of each symbol caused byfading in antenna 1 and Δ_(ant2), H_(ant2,0)˜H_(ant2,9) are the channelshift and channel response of each symbol caused by fading in antenna 2.The averaged de-patterning output for antenna 1 is A²·Δ_(ant1)/2, andthe averaged de-patterning output for antenna 2 isA²·(2H_(ant2,0)+9Δ_(ant2))/10.

Methods and apparatuses capable of more accurate interference estimationin high speed environments are thus desirable.

BRIEF SUMMARY OF INVENTION

The invention provides interference estimation circuits and methods forestimating interference in a received signal.

According to an aspect of the invention, an interference estimationcircuit for estimating interference of a received signal comprises asignal generator, a first symbol extractor and a first mixer. The signalgenerator generates an orthogonal signal orthogonal to partial symbolsof a plurality of pilot signals of the received signal. The first symbolextractor extracts partial symbols of a first decoded signal decodedfrom the received signal and outputs a first extracted signal whereinthe first decoded signal contains one of the plurality of pilot signals.The first extracted signal is substantially orthogonal to the orthogonalsignal. The first mixer is coupled to the signal generator for receivingthe orthogonal signal and to the first symbol extractor for receivingthe first extracted signal, and outputs a first mixed signal of theorthogonal signal and the first extracted signal for interferenceestimation.

The interference estimation circuit further comprises a decoder, asecond symbol extractor and a second mixer. The decoder separates thereceived signal into the first decoded signal and a second decodedsignal. The second symbol extractor extracts partial symbols of thesecond decoded signal and outputs a second extracted signal wherein thesecond decoded signal contains one of the plurality of pilot signals.The second extracted signal is substantially orthogonal to theorthogonal signal. The second mixer is coupled to the signal generatorfor receiving the orthogonal signal and to the second symbol extractorfor receiving the second extracted signal, and outputs a second mixedsignal of the orthogonal signal and the second extracted signal forinterference estimation.

According to another aspect of the invention, an interference estimationcircuit for estimating interference of a received signal comprises asignal generator, a first symbol extractor and a first mixer. The signalgenerator generates an orthogonal signal substantially orthogonal to aplurality of pilot signals of the received signal. The first mixer iscoupled to the signal generator for receiving the orthogonal signal,receives a first decoded signal decoded from a received signal, andoutputs a first mixed signal of the orthogonal signal and the firstdecoded signal. The first decoded signal contains one of the pluralitypilot signals. The first symbol extractor is coupled to the first mixerfor receiving the first mixed signal, extracts partial symbols of thefirst mixed signal according to the orthogonality of the first decodedsignal and the orthogonal signal, and outputs a first extracted signalfor interference estimation.

The interference estimation circuit further comprises a decoder, asecond mixer and a second symbol extractor. The decoder separates thereceived signal into the first decoded signal and a second decodedsignal. The second mixer is coupled to the signal generator forreceiving the orthogonal signal and to the decoder for receiving thesecond decoded signal, and outputs a second mixed signal of theorthogonal signal and the second decoded signal. The second symbolextractor extracts partial symbols of the second mixed signal accordingto the orthogonality of the second decoded signal and the orthogonalsignal and outputs a second extracted signal for interferenceestimation.

According to another aspect of the invention, an interference estimationmethod comprises the following steps. Step 1110 separates the receivedsignal into a first decoded signal and a second decoded signal. Step1120 generates an orthogonal signal orthogonal to partial symbols of theplurality of pilot signals of the received signal. Step 1130 extractsfirst and second extracted signal containing partial symbols of thefirst and second decoded signal that is substantially orthogonal to theorthogonal signal. Step 1140 mixes the orthogonal signal and theextracted signals and outputs mixed signals for interference estimation.

According to another aspect of the invention, an interference estimationmethod comprises the following steps. Step 1210 separates the receivedsignal into a first decoded signal and a second decoded signal. Step1220 generates an orthogonal signal orthogonal to a plurality of pilotsignals of the received signal. Step 1230 mixes the orthogonal signaland the first decoded signal and outputting a first mixed signal, andmixes the orthogonal signal and the second decoded signal and outputtinga second mixed signal. Step 1240 extracts partial symbols of the mixedsignals according to the orthogonality of the decoded signals and theorthogonal signal and outputs extracted signals for interferenceestimation.

The received signal transmitted in accordance with antenna transmitdiversity contains at least one frame, each frame contains a pluralityof slots, and each slot contains a plurality of symbols. The extractedsignal is extracted from N symbols of M slot of each of the receivedsignal that is substantially orthogonal to the orthogonal signal whereinN and M are both positive integers. The symbols are extracted fromfirst-N-symbol of first-M-slot in each frame, central-N-symbol offirst-M-slot in each frame or last-N-symbol of first-M-slot in eachframe.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows that common pilot symbols are transmitted on 2 antennas, inWCDMA systems with transmit diversity mode.

FIG. 2 shows patterns of transmitted signals and despreading signals.

FIG. 3 shows one example of fading effect in a high speed environment.

FIG. 4 shows the block diagram of an interference estimation circuitaccording to an embodiment of the invention.

FIG. 5 shows the operation of the interference estimation circuit ofFIG. 4.

FIG. 6 shows the block diagram of an interference estimation circuitaccording to another embodiment of the invention.

FIG. 7 shows the operation of the interference estimation circuit inFIG. 6.

FIG. 8 shows selecting first 4 symbols per slot from a first and secondsignal.

FIG. 9 shows the block diagram of an interference estimation circuitaccording to another embodiment of the invention.

FIG. 10 shows the operation of the interference estimation circuit inFIG. 9.

FIG. 11 is a flow chart shown an interference estimation methodaccording to another embodiment of the invention.

FIG. 12 is a flow chart shown an interference estimation methodaccording to another embodiment of the invention

DETAILED DESCRIPTION OF INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 4 shows the block diagram of an interference estimation circuitaccording an embodiment of the invention. In FIG. 4, an interferenceestimation circuit 400 comprises a signal generator 410, a first symbolextractor 420, a first mixer 430 coupled to the output of the signalgenerator 410 and to the output of the first symbol extractor 420, anintegrate & dump circuit 440 coupled to the first mixer 430, and asquare/average circuit 450 coupled to the integrate & dump circuit 440.The signal generator 410 generates an orthogonal signal, which isorthogonal to partial symbols of a plurality of pilot signals. Theplurality of pilot signals comprises control signals or a set ofpatterns known by the receiver. There are a number of well-known methodsfor selecting symbols and signals orthogonal to selected partial symbolsof pilot signals. In embodiments of this invention, the signal generator410 could utilize any known method for generating such an orthogonalsignal. The first symbol extractor 420 extracts partial symbols of areceived signal R wherein the received signal R contains pilot signals.The first symbol extractor 420 comprises an input node for receiving thereceived signal R, an output node for outputting an extracted signal.Neglecting the unexpected interference existing in the extracted signal,the extracted signal is substantially orthogonal to the orthogonalsignal generated by the signal generator 410. It should be noted thatthe invention uses the orthgonality between a pure signal and theorthogonal signal to cancel the pure signal, so it is still robust evenin such a situation that the unexpected interference existing in theextracted signal is bigger than the pure signal existing in theextracted signal. The first mixer 430 outputs a mixed signal of theorthogonal signal and the extracted signal. In theory, the mixed signalfrom the first mixer 430 shall contain no pure signal but interferenceand noise signal. The following integrate & dump circuit 440 and thesquare/average circuit 450 process the mixed signal for interferenceestimation

Further detailed illustration of the foregoing operation of theembodiment shown in FIG. 4 is shown in FIG. 5. In FIG. 5, the transmitsignal 51 is transmitted in a fading channel having channel response Hand channel shift Δ. After the fading channel effect, each symbol of thereceived signal 52 has different interference. The extracted signal 53is extracted by the symbol extractor 420 from the received signal 52. Ingeneral, a transmit signal contains a plurality of slots in one frameand a plurality of symbols in one slot. Thus, a selected partial pilotsignal, contains N symbols of M slots, is substantially orthogonal to anorthogonal signal generated at the receiver. N and M are both positiveintegers, for example, the central-8-symbol of 1 slot is used to denote8 symbols which centrally reside in one slot. The orthogonal signal 54generated by the signal generator 410 is orthogonal to some selectedpartial symbols of the plurality of pilot signals in the transmitsignal, for example (A, −A, A, −A). Note that the pattern selected isnot unique. For example, (A, A, −A, −A) is another candidate. Thecharacter, “A” or “−A”, represents a symbol in each signal. The symbollevel signal is decoded from a received signal and is provided forillustration only. The foregoing process can be performed at the chiplevel or other. The extracted signal 53 and the orthogonal signal 54 aresent to the first mixer 430, and then the mixed signal 55 is processedby the integrate & dump circuit 440 and the square/average circuit 450for interference estimation

FIG. 6 shows the block diagram of an interference estimation circuitaccording to another embodiment of the invention. In FIG. 6, aninterference estimation circuit 600 comprises a decoder 602, a signalgenerator 610, a first symbol extractor 620, a second symbol extractor622, a first mixer 630, a second mixer 632, an integrate & dump circuit640, a square/average circuit 650, an integrate & dump circuit 642 and asquare/average circuit 652. In a practical communication system, forexample, in the CDMA system, the transmit diversity technique istypically utilized to reduce the fading effect. The decoder 602separates the received signal R into a first decoded signal and a seconddecoded signal by orthogonal patterns corresponding to each transmittingantenna, respectively. The signal generator 610 generates an orthogonalsignal orthogonal to partial symbols of a plurality of pilot signals.The plurality of pilot signals is control signals or a set of patternsknown by the receiver. There are a number of well-known methods forselecting symbols and signals orthogonal to selected partial symbols ofpilot signals. In embodiments of this invention, the signal generator610 could utilize any known method for generating such an orthogonalsignal.

The first symbol extractor 620 and the second symbol extractor 622extract partial symbols of the first decoded signal and the seconddecoded signal, respectively. Assuming the received signal R contains atleast two mutual orthogonal pilot signals, the first decoded signalcontains one of pilot signals, and the second decoded signal containsanother one of pilot signals. Each of the first symbol extractor 620 andthe second symbol extractor 622 comprises an input node for receivingthe received signal R, an output node for respectively outputting afirst extracted signal and a second extracted signal. The first mixer630 outputs a first mixed signal of the orthogonal signal and the firstextracted signal. The second mixer 632 outputs a second mixed signal ofthe orthogonal signal and the second extracted signal. The followingintegrate & dump circuit 640 and the square/average circuit 650 processthe first mixed signal for interference estimation. The followingintegrate & dump circuit 642 and the square/average circuit 652 processthe second mixed signal for interference estimation.

Further detailed illustration of the foregoing operation of embodimentshown in FIG. 6 is shown in FIG. 7. In FIG. 7, the transmit signal 71 istransmitted in a fading channel having channel response H₁ and channelshift Δ₁ and the transmit signal 72 is transmitted in a fading channelhaving channel response H₂ and channel shift Δ₂. After decoding and thefading channel effect, each symbol of the first and second decodedsignals 73 and 74 has different levels of interference. The first andsecond extracted signal 75 and 76 are extracted by the first and secondsymbol extractor 620 and 622, respectively. The orthogonal signal 77generated by the signal generator 610 is orthogonal to the selectedpartial symbols of the plurality of pilot signals in the first andsecond transmit signals, for example (A, −A, A, −A). Note that thepattern selection is not unique. For example, (A, A, −A, −A) is anothercandidate. The characters, “A” or “−A”, represent a symbol in eachsignal. The symbol level signal is only for illustration, certainly, theforegoing process can be done in chip level or else. The first andsecond extracted signal 75 and 76 and the orthogonal signal 77 are sentto the first and second mixer 620 and 622, respectively. The first andsecond mixed signal 78, 79 are processed by the first and secondintegrate & dump circuit 640 and 642 as well as subsequently the firstand second square/average circuit 650 and 652 for interferenceestimation, respectively.

An extracted signal extracted by a symbol extractor is partial symbolsof a signal, and there are a number of methods for selecting partialsymbols from the signal. In general, a transmit signal contains aplurality of slots in one frame and a plurality of symbols in one slot.Thus, a selected partial pilot signal, contains N symbols of M slots, issubstantially orthogonal to an orthogonal signal generated at thereceiver. N and M are both positive integers, for example, thecentral-N-symbol of the M slots or first-N-symbol of M slots could beselected in the embodiments according to the invention. Further, thepatterns of the signal continuously crossing frame boundary (e.g.,Slot14-Slot0, in FIG. 8) or slot boundary (e.g., Symbol 9-Symbol 0, inFIG. 8) may be different from those patterns selected in the same slot,thus, a special process is required while the selected M slots crossingthe frame boundary or the slot boundary. In order to prevent the problemof crossing the frame boundary, the value of M can be a factor of thenumber of slots in one frame.

In practice, better methods, in accordance with some kinds of thecommunication specifications, for specific communication systems exist.For example, in a CDMA communication system with transmit diversitymode, a way for selecting partial symbols of a signal transmitted by aCDMA common pilot channel is to select first-4-symbols per slot. Forthose embodiments in accordance with 3GPP WCDMA specification, eachsymbol consists of 512 chips. As shown in FIG. 8, a first and secondtransmit signal 81, 82 are transmitted by antenna 1, 2, respectively.After decoding and respective fading channel effect, each symbol of afirst and second decoded signal 83 and 84 has different interference.Further a first and second extracted signal 85 and 86 is extracted basedon the foregoing selecting way.

FIG. 9 shows the block diagram of an interference estimation circuit 900according to another embodiment of the invention. In FIG. 9, aninterference estimation circuit 900 comprises a decoder 902, a signalgenerator 910, a first symbol extractor 920, a second symbol extractor922, a first mixer 930, a second mixer 932, an integrate & dump circuit940, a square/average circuit 950, an integrate & dump circuit 942 and asquare/average circuit 952. In a practical communication system, forexample, in the CDMA system, the transmit diversity technique istypically used to reduce the fading effect. The decoder 902 separatesthe received signal R into a first decoded signal and a second decodedsignal by orthogonal patterns corresponding to each transmittingantenna, respectively. The signal generator 910 generates an orthogonalsignal substantially orthogonal to a plurality of pilot signals. Theorthogonal signal is orthogonal to most bits of the pilot signals, forexample 80% of the bits. The plurality of pilot signals control signalsor a set of patterns known by the receiver. There are a number ofwell-known methods for selecting symbols and signals orthogonal toselected partial symbols of pilot signals. In embodiments of thisinvention, the signal generator 910 could utilize any known method forgenerating such an orthogonal signal.

The first decoded signal contains one of pilot signals, and the seconddecoded signal contains another one of pilot signals. The first mixer930 outputs a first mixed signal of the orthogonal signal and the firstdecoded signal. The second mixer 932 outputs a second mixed signal ofthe orthogonal signal and the second decoded signal. The first andsecond symbol extractor extract partial symbols of the first and secondmixed signal according to the orthogonality of the first and seconddecoded signal and the orthogonal signal, respectively. The followingintegrate & dump circuit 940 and the square/average circuit 950 processthe first extracted signal for interference estimation. The followingintegrate & dump circuit 942 and the square/average circuit 952 processthe second extracted signal for interference estimation.

Further detailed illustration of the foregoing operation of embodimentshown in FIG. 9 is shown in FIG. 10. For example, in a CDMAcommunication system with transmit diversity mode, antennas 1 and 2respectively transmit a first and second transmit signal 101 and 102through common pilot channel. After decoding and respective fadingchannel effect, each symbol of a first and second decoded signal 103 and104 has a different interference level. The signal generator 910generates an orthogonal signal 105. The first and second mixer 930 and940 mix the orthogonal signal 105 and a first and second decoded signal103 and 104, and outputs a first and second mixed signal 106 and 107,respectively. For those embodiments in accordance with 3GPP WCDMAspecification, each symbol consists of 512 chips. The first and secondsymbol extractor 920 and 922 extract the first-4-symbols per slot fromthe first and second mixed signal 106, 107 according to theorthogonality of the first and second decoded signal 103 and 104 and theorthogonal signal, and output a first and second extracted signal 108and 109, respectively. Another method for extracting partial symbolsselects the first-N-symbol of the M slots of the signal, for example thefirst-14-symbols of the first 3 slots in a frame.

FIG. 11 is a flow chart shown an interference estimation method 1100according to another embodiment of the invention. For estimatinginterference of a received signal transmitted in accordance with antennatransmit diversity, step 1110 separates the received signal into a firstdecoded signal and a second decoded signal. Step 1120 generates anorthogonal signal orthogonal to partial symbols of the plurality ofpilot signals of the received signal. Step 1130 extracts first andsecond extracted signal containing partial symbols of the first andsecond decoded signal that is substantially orthogonal to the orthogonalsignal. Step 1140 mixes the orthogonal signal and the extracted signalsand outputting mixed signals for interference estimation.

FIG. 12 is a flow chart shown an interference estimation method 1200according to another embodiment of the invention. For estimatinginterference of a received signal transmitted in accordance with antennatransmit diversity, step 1210 separates the received signal into a firstdecoded signal and a second decoded signal. Step 1220 generates anorthogonal signal orthogonal to a plurality of pilot signals of thereceived signal. Step 1230 mixes the orthogonal signal and the firstdecoded signal and outputting a first mixed signal, and mixes theorthogonal signal and the second decoded signal and outputting a secondmixed signal. Step 1240 extracts partial symbols of the mixed signalsaccording to the orthogonality of the decoded signals and the orthogonalsignal and outputs an extracted signal for interference estimation.

In methods 1100 and 1200, the received signal contains at least oneframe, each frame contains a plurality of slots, and each slot containsa plurality of symbols. The extracted signal is extracted from N symbolsof M slot of each of the received signal that is substantiallyorthogonal to the orthogonal signal wherein N and M are both positiveintegers. The symbols are extracted from first-N-symbol of first-M-slotin each frame, central-N-symbol of first-M-slot in each frame orlast-N-symbol of first-M-slot in each frame.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. An interference estimation circuit, for estimating interference of areceived signal, comprising: a signal generator, for generating anorthogonal signal orthogonal to partial symbols of a plurality of pilotsignals of the received signal; a first symbol extractor, for extractingpartial symbols of a first decoded signal decoded from the receivedsignal and outputting a first extracted signal, wherein the firstdecoded signal contains one of the plurality of pilot signals, whereinthe first extracted signal is substantially orthogonal to the orthogonalsignal; and a first mixer, coupled to the signal generator for receivingthe orthogonal signal, coupled to the first symbol extractor forreceiving the first extracted signal, outputting a first mixed signal ofthe orthogonal signal and the first extracted signal for interferenceestimation.
 2. The interference estimation circuit of claim 1, whereinthe first decoded signal contains at least one frame, each framecontains a plurality of slots, and each slot contains a plurality ofsymbols, wherein the first symbol extractor extracts N symbols of M slotof each frame that are substantially orthogonal to the orthogonalsignal, where N and M are both positive integers.
 3. The interferenceestimation circuit of claim 2, wherein the symbols are extracted fromone of the following groups: first-N-symbol of first-M-slot in eachframe; central-N-symbol of first-M-slot in each frame; and last-N-symbolof first-M-slot in each frame.
 4. The interference estimation circuit ofclaim 1, wherein the received signal is transmitted in accordance withantenna transmit diversity.
 5. The interference estimation circuit ofclaim 1, further comprising: a decoder, for separating the receivedsignal into the first decoded signal and a second decoded signal; asecond symbol extractor, for extracting partial symbols of the seconddecoded signal and outputting a second extracted signal, wherein thesecond decoded signal contains one of the plurality of pilot signals,wherein the second extracted signal is substantially orthogonal to theorthogonal signal; and a second mixer, coupled to the signal generatorfor receiving the orthogonal signal, coupled to the second symbolextractor for receiving the second extracted signal, outputting a secondmixed signal of the orthogonal signal and the second extracted signalfor interference estimation.
 6. An interference estimation circuit, forestimating interference of a received signal, comprising: a signalgenerator, for generating an orthogonal signal substantially orthogonalto a plurality of pilot signals of the received signal; a first mixer,coupled to the signal generator for receiving the orthogonal signal,wherein the first mixer further configured for receiving a first decodedsignal decoded from the received signal and outputting a first mixedsignal of the orthogonal signal and the first decoded signal, whereinthe first decoded signal contains one of the plurality pilot signals;and a first symbol extractor, coupled to the first mixer for receivingthe first mixed signal, extracting partial symbols of the first mixedsignal according to the orthogonality of the first decoded signal andthe orthogonal signal, and outputting a first extracted signal forinterference estimation.
 7. The interference estimation circuit of claim6, wherein the mixed signal contains at least one frame, each framecontains a plurality of slots and each slot contains a plurality ofsymbols, wherein the first symbol extractor extracts N symbols of M slotof each frame that are substantially orthogonal to the orthogonal signalfrom the mixed signal, where N and M are both positive integers.
 8. Theinterference estimation circuit of claim 7, wherein the symbols areextracted from one of the following groups: first-N-symbol offirst-M-slot in each frame; central-N-symbol of first-M-slot in eachframe; and last-N-symbol of first-M-slot in each frame.
 9. Theinterference estimation circuit of claim 6, wherein the received signalis transmitted in accordance with antenna transmit diversity.
 10. Theinterference estimation circuit of claim 6, further comprising: adecoder, for separating the received signal into the first decodedsignal and a second decoded signal; a second mixer, coupled to thesignal generator for receiving the orthogonal signal and coupled to thedecoder for receiving the second decoded signal, wherein the secondmixer further configured for outputting a second mixed signal of theorthogonal signal and the second decoded signal; and a second symbolextractor, coupled to the second mixer for receiving the second mixedsignal, extracting partial symbols of the second mixed signal accordingto the orthogonality of the second decoded signal and the orthogonalsignal, and outputting a second extracted signal for interferenceestimation.
 11. An interference estimation method, for estimatinginterference of a received signal, comprising: generating an orthogonalsignal orthogonal to partial symbols of a plurality of pilot signals ofthe received signal, extracting a first extracted signal containingpartial symbols of a first decoded signal decoded from the receivedsignal that is substantially orthogonal to the orthogonal signal; andmixing the orthogonal signal and the first extracted signal foroutputting a first mixed signal for interference estimation.
 12. Theinterference estimation method of claim 11, wherein the received signalcontains at least one frame, each frame contains a plurality of slots,and each slot contains a plurality of symbols, wherein the extractedsignal is extracted from N symbols of M slot of each of the receivedsignal that is substantially orthogonal to the orthogonal signal, whereN and M are both positive integers.
 13. The interference estimationmethod of claim 12, wherein the symbols are extracted from one of thefollowing groups: first-N-symbol of first-M-slot in each frame;central-N-symbol of first-M-slot in each frame; and last-N-symbol offirst-M-slot in each frame.
 14. The interference estimation method ofclaim 11, wherein the received signal is transmitted in accordance withantenna transmit diversity.
 15. The interference estimation method ofclaim 11, further comprising: separating the received signal into thefirst decoded signal and a second decoded signal; extracting an secondextracted signal containing partial symbols of the second decoded signalthat is substantially orthogonal to the orthogonal signal; and mixingthe orthogonal signal and the second extracted signal for outputting asecond mixed signal for interference estimation.
 16. An interferenceestimation method, for estimating interference of a received signal,comprising: generating an orthogonal signal orthogonal to a plurality ofpilot signals of the received signal; mixing the orthogonal signal and afirst decoded signal decoded from the received signal for outputting afirst mixed signal, wherein the first decoded signal contains one of theplurality of pilot signals; and extracting an extracted signalcontaining partial symbols of the first mixed signal according to theorthogonality of the first decoded signal and the orthogonal signal andoutputting the first extracted signal for interference estimation. 17.The interference estimation method of claim 16, wherein the first mixedsignal contains at least one frame, each frame contains a plurality ofslots, and each slot contains a plurality of symbols, wherein the firstextracted signal is extracted from N symbols of M slot of each of thefirst mixed signal that is substantially orthogonal to the orthogonalsignal, where N and M are both positive integers.
 18. The interferenceestimation method of claim 17, wherein the symbols are extracted fromone of the following groups: first-N-symbol of first-M-slot in eachframe; central-N-symbol of first-M-slot in each frame; and last-N-symbolof first-M-slot in each frame.
 19. The interference estimation method ofclaim 16, wherein the received signal is transmitted in accordance withantenna transmit diversity.
 20. The interference estimation method ofclaim 16, further comprising: separating the received signal into thefirst decoded signal and a second decoded signal; mixing the orthogonalsignal and the second decoded signal for outputting a second mixedsignal, wherein the second decoded signal contains one of the pluralityof pilot signals; and extracting the second extracted signal containingpartial symbols of the second mixed signal according to theorthogonality of the second decoded signal and the orthogonal signal andoutputting the second extracted signal for interference estimation.